The Coast Guard is investigating why there seemed to be no warning before the 332-foot megayacht Attessa IV, one of the largest private yachts in the world, hit the 65-foot charter fishing boat Prowler at night in the Pacific south of San Diego, killing one man on the fishing boat. The Coast Guard said the accident occurred about 7 p.m. nine miles off Imperial Beach near the U.S.-Mexico border. Prowler was on its way back to its home base in San Diego after a fishing trip in Mexican waters. Attessa hit the starboard quarter of Prowler, causing extensive damage, and critically injuring Richard…